The invention relates to above ground liquid storage containers and, more specifically, to a composite above ground liquid storage container, also known as a vault, which incorporates features that enable the detection of fluid leaking from the primary containment cavity of the vault.
The interest in the safe containment of hazardous liquids, particularly volatile fuels such as gasoline, is a continuous one. Previously, these liquids were stored in large capacity underground tanks. The various reasons for using underground or buried tanks have included eliminating the possibility that the tank would be ruptured by a vehicle during an accident; reducing the inherent fire risks associated with volatile liquid storage by insulating the storage vessel from an external heat source or fire; and neutralizing leaked liquid by having it absorbed into the surrounding soil thereby reducing the risk of a contaminated ground surface, a potential fire and various other health and safety risks.
It has become increasingly apparent that the risks associated with leaking underground storage tanks can, and often do, outweigh the benefits of underground storage and can outweigh the risks associated with above ground storage. Underground storage tank leaks have been found to have serious short term and long term environmental consequences. The widespread use of underground storage and the known and potential liabilities have lead to the inspection, removal and replacement of numerous leaking storage tanks. With the cost of inspecting, removing and replacing the underground tank being quite high in and of itself, the expense escalates if it is found that the surrounding soil has been contaminated and requires environmental reclamation.
Once a leaking tank has be identified and the associated cleanup has been completed, businesses are now considering the various alternatives to burying another tank. One alternative is the above ground storage vault.
Above ground storage tanks must meet stringent Environmental Protection Agency (EPA) regulations. These regulations vary widely and depend on the particular liquid being stored. Additionally, again depending on the specific liquid to be contained within the vault, the regulations promulgated by the National Fire Protection Association and the Uniform Fire Code must also be met. While the regulations vary from liquid to liquid, some common safety requirements include, but are not limited to, insulation from extreme external heat sources and resistance to natural and man-made physical disasters such as earthquakes and vehicle accidents.
A variety of storage tank which has been used both above and below ground is the double walled or dual containment tank. Typically, dual containment tanks include an inner tank for primary liquid containment and an outer tank providing secondary containment. A space is generally provided between the inner and outer tanks and is used to monitor the inner tank for leaks.
In some dual containment tanks, the space between the inner and outer tanks is filled with one or more materials offering additional insulating and/or structural support to the tank. These tanks are commonly known as storage vaults and concrete is often on of the interdisposed materials. The present invention is a variant of this type of storage vaults.
One of the primary objects of this invention is to provide an above ground storage vault with a dual containment construction in which a space between the two tanks can be monitored for leaks. The present invention also provides a storage vault in which the space between the inner and outer tanks is at least partially filled with a material that serves both an insulating and structural function.
To achieving these and other objects, the present invention provides an above ground liquid storage vault having a composite construction. The vault is generally constructed of an inner tank and an outer tank. The inner tank defines a primary containment cavity which is adapted to receive and store a liquid, such as gasoline. The inner tank includes an inlet fitting, a discharge fitting and a vent, all of which extend to positions exterior of the vault. Additional fittings, if desired, can be provided on the vault as determined by the particular application to which the vault will be applied.
Before being positioned within the outer tank, the inner tank is first encapsulated in a layer of an insulating material. In addition to insulating the liquid in the inner tank, the first layer is made of a material which will at least partially dissolve, melt or otherwise liquify upon contact with any leaked liquid from the inner tank.
A monitor tube is positioned immediately exterior of this first layer and extends from a leak collection region, located near the bottom of the inner tank, to a position exterior of the outer tank. If a leak does occurs in the inner tank, a portion of the first layer near the leak will dissolve and the leaked liquid will be allowed to naturally progress to the leak collection area where it will be detected by manual or automated monitoring through the monitor tube.
After the inner tank has been encapsulated within the insulating material, both the inner tank and the insulating material, as well as the monitor tube, are further encapsulated by a membrane. Unlike the insulating layer, the membrane is impervious to the specific liquid being stored and does not react or dissolve when it comes into contact with leaked liquid. The membrane therefore provides a barrier to further leakage from the vault.
The encapsulated inner tank, as so far described, is then positioned within the cavity of the outer tank. In positioning the encapsulated inner tank within the outer tank, the encapsulated inner tank is supported on spacers in the outer tank which provide a space or gap between the interior surfaces of the outer tank and the exterior surfaces of the encapsulated inner tank. This space is filled with a structural and insulating material which further covers the bottom, sides and top of the inner tank. In one preferred embodiment of this invention, the structural and insulating material is concrete.
Hold-down members extend between the side walls of the outer tank across the top of the encapsulated inner tank so as to prevent the inner tank from floating on the poured concrete. The top wall of the outer tank is secured to the side walls of the outer tank by welding or some other securement method and is provided with an opening through which the concrete may be poured once the vault has been delivered to its site o usage.
Since the composite vault is to be used above ground and, most likely outdoors, the exterior surface of the outer tank is coated with an anti-corrosion material which protects the outer tank and enhances the aesthetic appearance of the vault. Reinforced fiberglass is one material which meets the criteria for the anti-corrosion material.
The vault is also provided with bottom supports or risers which raise the vault several inches above the surface on which it is supported. These risers allow the surface beneath the vault to be visually inspected for further evidence of leakage and also enable the vault to be anchored to the support surface.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.